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Nitrogen Solubility Index (NSI) of Canola Seed and Meal Produced at Canadian and Japanese Crushing Plants.

J. Daun and M. Kisilowsky

Canadian Grain Commission Grain Research Laboratory
1404-303 Main St. Winnipeg, MB R3C 3G8 Canada
Phone: 204 983 3350 Fax: 204 983 0724 Email: jdaun@cgc.ca

Abstract

The solubility of nitrogen (NSI) in caustic solution is a good indicator of the degree of processing in oilseed meals and has been directly linked to amino acid availability in some studies. Canola seed and meal samples were extracted in 0.5% KOH. The extracted nitrogen was determined with a LECO FP-428 Nitrogen Determinator with a RMSD of 3 NSI. NSI were determined for samples of meals and seed from four Canadian and four Japanese processing plants from 1993-1995. The NSI of the seed ranged from 64-85 with no differences between plants or countries. Among the meals, the NSI ranged 36-69 with no differences between countries. There were significant differences in NSI’s between processing plants with one plant averaging 67 NSI being significantly higher than the other plants..

Keywords: combustion protein processing methodology Dumas

Introduction

Canola meal is high in dietary protein which makes it a favorable supplement in animal feed rations. During processing, and particularly during desolventizing-toasting, canola meal undergoes extensive heating which affects the protein solubility (measured as nitrogen solubility) and the amino acid availability of the end product (Anderson-Hafermann, J.C. and Y. Zhang, 1992). The nitrogen solubility of soybeans has been assessed using 0.2% KOH but it has been shown that the use of 0.5% KOH is better for evaluating canola (Parsons et al., 1990). In previous studies, after protein extraction in 0.5% KOH, the nitrogen was determined by the traditional Kjeldahl method, (Parsons et al., 1990, AOCS Ba 11-65 (93)). Since the combustion method has been accepted in determining nitrogen in oilseeds (AOCS Ba 4e-93 (95)) it was thought that this method could be used as the basis for a method for determination of NSI in canola meal.

This study applied the Dumas combustion method to the determination of the NSI for canola meals and applied the method to the evaluation of seeds and commercial meals from Canadian and Japanese crushing facilities.

Materials and Methods

Nitrogen solubility index (NSI) was determined by modifying accepted procedures (AOCS 1990, Daun and DeClercq, 1994) . Both meal and seed samples were ground on a coffee mill and then defatted with petroleum ether using a Soxtec (Tecator) extractor(AOCS Am2-93(95)). Meals were extracted without the regrinding steps.

Nitrogen was extracted from the ground, defatted flour by placing approximately 1.5 g into a 200 ml beaker and adding 75 ml of 0.5% KOH. The mixture was stirred for 20 minutes at 120 rpm using a magnetic stir bar while maintaining the solution at 30 C. A subsample of approximately 50 ml was then centrifuged at 2000 rpm for 10 minutes. A 3cc aliquot of supernatant was collected and filtered through a 0.45μ filter using a syringe. Filtration was necessary in order to obtain a clear solution which improved the precision given the small aliquot tested for nitrogen. Nitrogen was determined on duplicate samples of by weighing (to .001 g) 0.500 ml of filtered supernatant into a tin cup and determining nitrogen on a LECO FP-428 Nitrogen Determinator3.

Nitrogen was also determined on the 150 mg duplicate samples of defatted dry matter of each sample. The samples were dried overnight in a forced air oven at 105 degree Celsius

The NSI was calculated as follows: NL/ND x 50 x 100 = NSI where:

NL = nitrogen from liquid sample (mean of two determinations)

ND = nitrogen from seed or meal before extraction (mean of tow determinations)

50 = dilution factor

Samples of seed and meal processed from the seed were obtained from crushing plants in Canada and Japan between 1993 and 1996.

Results And Discussion

Analysis of duplicate meal samples (Table 1) showed that the method was repeatable with a RMSD (root mean square deviation) of 3.1 NSI (repeatability 8.7 NSI). This repeatability is considerably greater than the 3.7 suggested by the AOCS method possibly due to the combined effects of miniaturization used in this study. For example, the RMSD for repeated measures of nitrogen (i.e. repeated 0.500-mL aliquots from the same sample) was about 0.003 for measures ranging from 0.028 to 0.12. If the method were to be adapted as a replacement for the official method, increasing the amount of nitrogen determined would probably result in significant improvement of the repeatability. The ratio of flour to extract could be increased more than 5 times without changing the relative amount of nitrogen extracted (Figure 1). The method, without increasing the flour/extract ratio, was adequate for the study on the variability of NSI within and between different canola crushing plants.

Table 1. Repeated measures of NSI content of commercial meal samples.

Sample

Rep A

Rep B

Diff

807

49.2

52.3

3.1

794

56.5

52.4

-4.0

693

50.7

49.3

-1.5

692

66.4

68.0

1.6

720

63.7

59.7

-4.0

   

RMSD1

3.06

Increasing the concentration of KOH resulted in an increase in the amount of nitrogen extracted, particularly in the case of processed meals (Table 2).

Figure 1. Effect of increasing flour extract ratio on extracted nitrogen.

Table 2. Effect of increasing concentration of KOH on NSI.

Sample

NIS in Meal (%)

NSI in Seed (%)

KOH

0.2%

0.5%

0.2%

0.5%

706m

50.0

68.5

87.1

85.5

707m

31.4

35.9

68.4

75.4

725m

27.0

44.4

76.4

80.2

778m

18.1

39.3

75.0

76.5

796m

41.5

48.2

80.1

81.6

799m

36.7

51.6

82.0

84.4

805m

41.1

51.2

82.7

83.5

811m

20.9

43.3

77.3

82.0

Mean

33.4

47.8

78.6

81.1

Difference

14.44

 

2.52

Prob. T

 

0.0005

 

0.030

Analysis of variance showed that there was no significant difference in the NSI values for seeds between countries or plants. This is not surprising since both Canadian and Japanese crushing plants drew virtually all of their seed from Western Canada during the period studied. The NSI values for seed ranged from 64 to 86 but no particular pattern could be discerned. While previous work at this laboratory (Daun et al. 1993) demonstrated that bin-heating reduced NSI in canola seed, it is unlikely that the seed in this study was sufficiently damaged to show this type of effect. More work is required to determine the reason for this range in results.

There was a significant difference between plants but not between countries for the NSI values for meals with Japanese plant 4 having higher NSI meal values than the other plants. Multiple means comparison (Duncan) showed that the other plants fell into three overlapped groupings (NSI 41 to 44, NSI 42 to 48 and NSI 48 to 52). The NSI values for seed ranged from 36 to 67 and there was considerable variability in the NSI values for meals within some plants suggesting variability in process conditions.

Processing reduced NSI. This reduction ranged from a low of 10 NSI in Japanese plant 4 to a high of 36 NSI for Japanese plant 2 with other plants showing a reduction of 24 to 30. There was no relationship between the seed NSI and the meal NSI.

The results of this study demonstrate that the Dumas combustion method can be applied to the determination of NSI on canola seeds and meals. More work will be required, however, to improve the sensitivity and hence the repeatability of the method before it can be considered as a routine method. Application of the procedure to seeds and meals from crushing plants demonstrated that there was a wide range of NSI in products from both Japanese and Canadian crushing plants indicating a wide variability in the quality of meal available. Some plants were able to produce meals with consistent, high levels of NSI indicating that it meal quality can be maintained if it is made a process concern.

Table 3. Nitrogen Solubility Index of Seed and Meal from Canadian and Japanese Crushing Plants.

Canadian Plant

Sample Date

NSI Meal

NSI Seed

Japanese Plant

Sample Date

NSI Meal

NSI Seed

1

April-95

47.6

70.6

1

September-93

50.7

64.2

1

August-95

51.6

84.4

1

October-93

43.9

69.1

1

February-96

58.7

69.7

1

November-93

35.9

75.4

1

March-96

46.2

74.9

1

February-94

37.0

74.7

 

Mean

51.0

74.9

   

41.9

70.9

2

February-94

47.7

64.4

2

October-94

42.9

81.4

2

April-95

45.3

67.3

2

March-95

47.6

83.8

2

September-95

42.2

71.4

2

April-95

39.3

69.3

2

November-95

43.3

82.0

2

November-95

39.3

76.5

 

Mean

44.6

71.3

   

42.3

77.7

3

February-94

44.4

80.2

3

February-95

46.2

71.2

3

March-94

42.1

70.8

3

March-95

48.0

81.2

3

April-94

46.7

70.6

3

May-95

48.2

81.6

3

June-94

42.7

77.2

3

July-95

49.2

75.0

 

Mean

44.0

74.7

   

47.9

77.3

4

April-95

52.2

80.2

4

November-93

68.5

85.6

4

July-95

51.6

76.4

4

February-94

63.7

71.2

4

December-95

51.2

83.5

4

May-94

68.1

78.4

4

February-96

51.6

81.9

4

June-95

67.2

73.6

 

Mean

51.6

80.5

   

66.9

77.2

 

Mean All

47.8

75.3

   

49.7

75.8

References

1. Anderson-Hafermann, J.C. and Y. Zhang. Effects of Processing on the Nutritional Quality of Canola Meal. Poultry Science 72:326-333 (1992).

2. Daun, J. and D. DeClercq. Comparison of Combustion and Kjeldahl Methods for Determination of Nitrogen in Oilseeds. J. Amer. Oil Chem. Soc 71,:1069-1072(1994).

3. Daun, J.K., Buhr, N., Mills, J.T., Diosady, L.L. and Mag, T. Oilseeds -Processing. Chapter D-11, in Grains and Oilseeds, Handling, Marketing, Processing. Fourth Edition. Canadian International Grains Institute, Winnipeg, Volume II pp. 896-898(1993).

4. Firestone, D. (ed.). Official Methods and Recommended Practices of the American Oil Chemists' Society). AOCS Press, Champaign IL 1998.

5. Parsons, C.M., K. Hashimoto, K. J. Wedeking, and D. H. Baker. Soybean Protein Solubility in Potassium Hydroxide: An In Vitro Test of Vivi Protein Quality. Animal Science 69:2918-2924 (1990).

1 RMSD = Root mean squared deviation

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